Method of forming a battery and battery

ABSTRACT

A button-type battery includes, a) an anode; b) a cathode positioned adjacent to the anode; c) an electrolyte between the anode and the cathode; d) a conductive first terminal housing member in electrical contact with one of the anode or the cathode; the first terminal housing member having a periphery; e) a conductive second terminal housing member in electrical contact with the other of the anode or the cathode; the second terminal housing member having a periphery; f) the first and second terminal housing members forming an enclosed housing which holds and protects the anode, the cathode and the electrolyte; and g) the first and second terminal housing member peripheries being configured together to form an electrically insulative seal which seals the anode, the electrolyte and the cathode within the housing formed by the first and second terminal housing members, the electrically insulative seal comprising cross-linked butyl rubber. The seal can include a gasket which constitutes the cross-linked butyl rubber or other material. The seal can comprise an uncured precursor to butyl rubber. Methods of forming such button-type batteries include in situ curing or forming butyl rubber in place on one of the battery terminals. Alternately, a butyl rubber precursor can be applied to one or both of the battery terminals.

TECHNICAL FIELD

This invention relates to methods of forming button-type batteries andto button-type battery constructions.

BACKGROUND OF THE INVENTION

Button-type batteries are small, thin energy cells that are commonlyused in watches and other electronic devices requiring a thin profile. Aconventional button-type battery includes two electrodes in the form ofan anode and a cathode. These are typically separated by a porousseparator. An electrolyte is present within pores of the separator.

These internal battery components are housed within a metal casing orhousing formed by a lower conductive can and an upper conductive lid. Acommon prior art material for the can and lid is stainless steel. Thecan is typically in electrical contact with the cathode to form thepositive battery terminal, and the lid is in electrical contact with theanode to form the negative battery terminal. The can and lid are crimpedor pressed together to form a fluid-tight seal which entirely enclosesthe anode, cathode, separator, and electrolyte. An electricallyinsulating sealing gasket is provided within the primary seal betweenthe lid and can to electrically isolate the two housing members.

There is a need in button-type battery usage to make such energy cellsthinner. Today, the thinnest commercially available button-type batteryhas a thickness of 1.2 mm (47.2 mils). It would be desirable to make athinner battery, particularly one having a thickness of less than 1 mm(39.4 mils). A countering concern, however, is that the integrity of thefluid-tight seal cannot be compromised simply to achieve the goal ofthinner batteries.

One challenge in the fabrication of thin button cells concerns thebattery seal. Industry standard coin cell battery gaskets typicallyemploy an injection molded polymer gasket (i.e., polypropylene orpolyethylene). Minor imperfections and voids in the crimped gasket sealarea are normally filled by the application of a supplemental sealantmaterial, such as asphalt. However, conventional injection moldingtechnology is not easily adapted to ultra-thin button cell batteries dueto the minimum thickness of the gasket that can be cost effectivelyobtained. Further, water permeability of the seal becomes problematicwith thinner and thinner button cell gaskets and seals.

Accordingly, needs remain in the development of improved materials andmethods associated with button-type battery seals.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a cross-sectional view of an assembled button-type batteryconstruction.

FIG. 2 is an enlarged cross-sectional view of a peripheral sealingportion of the FIG. 1 assembly.

FIG. 3 is an enlarged cross-sectional view of a peripheral sealingportion of an alternate embodiment assembled button-type batteryconstruction.

FIG. 4 is a diagrammatic side sectional plan view of a processing stepin accordance with the invention.

FIG. 5 is a side cross-sectional view of a single battery terminalhousing member produced in accordance with methodical aspects of theinvention.

FIG. 6 is a top view of FIG. 5.

FIG. 7 is an enlarged, more-to-scale, cross-sectional, exploded view ofa 20 mm diameter battery preassembly utilizing the FIGS. 5 and 6 housingmember, and other components.

FIG. 8 is a cross-sectional view of the FIG. 7 assembly at a processingstep subsequent to that shown by FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

This invention concerns "coin" or "button-type" batteries also referredto as "button cells", and their components. A button-type battery istypically a small, circular-shaped energy cell approximately the size ofa small coin. The button-type battery can be constructed in differentsizes, with typical diameters being 12 mm, 16 mm, and 20 mm. Othershapes are possible, but the circular shape is most common.

In accordance with one aspect of the invention, a button-type batterycomprises:

an anode;

a cathode positioned adjacent to the anode;

an electrolyte between the anode and the cathode;

a conductive first terminal housing member in electrical contact withone of the anode or the cathode; the first terminal housing memberhaving a periphery;

a conductive second terminal housing member in electrical contact withthe other of the anode or the cathode; the second terminal housingmember having a periphery;

the first and second terminal housing members forming an enclosedhousing which holds and protects the anode, the cathode and theelectrolyte; and

the first and second terminal housing member peripheries beingconfigured together to form an electrically insulative seal which sealsthe anode, the electrolyte and the cathode within the housing formed bythe first and second terminal housing members, the electricallyinsulative seal comprising cross-linked butyl rubber.

In accordance with another aspect of the invention, the seal area of thebattery comprises a chemical precursor to formation of butyl rubber.

In accordance with another aspect of the invention, a method of forminga button-type battery comprises the following steps:

providing an electrically conductive first terminal housing membermaterial;

depositing an electrically insulative chemical precursor material toformation of butyl rubber relative to a sealing region of the firstterminal housing member material, the deposited precursor material beingvoid of any polymerizing or curative agents;

providing the first terminal housing member material into a shape of adesired first terminal housing member;

providing an electrically conductive second terminal housing member infacing juxtaposition to the first terminal housing member having thedeposited butyl rubber precursor material, the second terminal housingmember having a sealing region;

providing an anode and a cathode having an electrolyte positionedtherebetween; the anode, the cathode, and the electrolyte beingpositioned intermediate the juxtaposed first and second terminal housingmembers; the anode being positioned to electrically connect with one ofthe first or second terminal housing members and the cathode beingpositioned to electrically connect with the other of the first or secondterminal housing members; and

joining the sealing regions of the first and second terminal housingmembers together to form an enclosed battery housing retaining theanode, the cathode and the electrolyte; the electrically insulativebutyl rubber precursor material void of any polymerizing and curativeagents being interposed between the joined first and second terminalhousing members; the precursor material between the joined first andsecond terminal housing members comprising an electrically insulativefluid-tight seal therebetween.

In accordance with still a further aspect of the invention, a method offorming a button-type battery comprising the following steps:

providing an electrically conductive first terminal housing membermaterial;

depositing an uncured electrically insulative chemical precursormaterial to formation of butyl rubber relative to a sealing region ofthe first terminal housing member material, the deposited uncuredprecursor material comprising a curative and polymerizing agent capableof curing the material into polymerized cross-linked butyl rubber, themethod comprising in situ curing of the chemical precursor material intobutyl rubber;

providing the first terminal housing member material into a shape of adesired first terminal housing member;

providing an electrically conductive second terminal housing member infacing juxtaposition to the first terminal housing member having thedeposited butyl rubber precursor, the second terminal housing memberhaving a sealing region;

providing an anode and a cathode having an electrolyte positionedtherebetween; the anode, cathode, and electrolyte being positionedintermediate the juxtaposed first and second terminal housing members;the anode being positioned to electrically connect with one of the firstor second terminal housing members and the cathode being positioned toelectrically connect with the other of the first or second terminalhousing members; and

joining the sealing regions of the first and second terminal housingmembers together to form an enclosed battery housing retaining theanode, cathode and electrolyte comprising an electrically insulativefluid-tight seal therebetween; the insulative fluid tight sealcomprising in situ formed butyl rubber.

Referring first to FIGS. 1 and 2, a button-type battery is indicatedgenerally with reference numeral 10. Battery 10 has an anode 12, acathode 14, and a liquid electrolyte 16 between the anode and cathode. Aporous separator 17 is positioned between anode 12 and cathode 14 toohmically separate the anode and cathode and retain electrolytetherebetween.

Button-type battery 10 also includes a circular conductive first, lower,or bottom terminal housing member 18 which forms the can of the energycell. First terminal housing member 18 has a central portion 20 inelectrical contact with cathode 14 and a periphery 22 surroundingcentral portion 26. First housing member 18 defines a positive batteryterminal as it ohmically contacts cathode 14.

Battery 10 has a circular conductive second, upper, or top terminalhousing member 24 which forms the lid of the energy cell. Secondterminal housing member 24 has a central portion 26 in electricalcontact with anode 12 and a periphery 28 surrounding central portion 26.In ohmic connecting with anode 12, second housing member 24 defines anegative battery terminal. First and second terminal housing members 18and 24 combine to form an enclosed housing 30 which holds and protectsanode 12, cathode 14, and electrolyte 16.

Anode 12, cathode 14, electrolyte 16 and separator 17 can be formed ofconventional construction. For example, anode 12 can comprise elementallithium provided on a copper backed foil, and having a preferredthickness of approximately 2 mils (0.0508 mm). Cathode 14 can be formedof a compressed tablet made from a composite of manganese (IV) oxide,carbon, and teflon powder, and having a preferred thickness of 8 mils(0.2032 mm). An example electrolyte 16 comprises a solution of propylenecarbonate and ethylene glycol dimethylether, having dissolved lithiumtetrafluoroborate and dimethylether. The volume of electrolyte 16provided within first terminal housing member 18 at pre-assembly ispreferably gauged to fill the substantial void within housing member 18,yet not so great to leak upon crimp sealing of the battery assembly.

Separator 17 is preferably formed of a woven or porous polymericmaterial, such as polyethylene, polypropylene, or teflon. Separator 17preferably has unidirectional pores formed in the "Z" direction tofacilitate electrolytic conductivity between anode 12 and cathode 14. Anexample preferred thickness for separator 14 is 1 mil (0.0254 mm).

First and second terminal housing members 18 and 24 are preferablyformed of a conductive material having a thickness of less than 8 mils(0.2032 mm), with a thickness in a range of approximately 3-5 mils(0.0762-0.1270 mm) being more preferred. An example material used forthe terminal housing members is type 304 stainless steel.

First and second terminal housing member peripheries 22 and 28 areconfigured together to form an electrically insulative seal which sealsanode 212, electrolyte 16, and cathode 14 within housing 30 formed byfirst and second terminal housing members 18 and 24. In one preferredembodiment, electrically insulative seal 32 comprises crosslinked butylrubber material 34. Preferably, the electrically insulative portion ofseal 32 consists essentially of a butyl rubber material. Such can beprovided in the form of a pre-formed gasket which is placed within firstterminal housing member 18 immediately prior to assembly. Alternately,butyl rubber material can be formed in situ relative to second terminalhousing member 18 either before or after member 18 is formed into adesired shape. Example methods of construction are further describedbelow. Ideally where a goal is to produce a thinnest possible battery,the FIGS. 1 and 2 construction will have a total combined thickness ofless than 1 mm. Butyl rubber in use in a sealing gasket for abutton-type battery provides advantages of significant water resistance,and a high compression set resistance which does not cold flow or relaxunder compressive forces of the battery crimp.

FIG. 3 illustrates an alternate embodiment electrically insulative seal32a. Like numerals from the first described embodiment are utilizedwhere appropriate, with differences being indicated by differentnumerals or with the suffix "a". Here, seal 32a of button-type battery10a comprises a pre-formed gasket material 34a which consistsessentially of a polymer which is not butyl rubber. Examples includepolyethylene, polypropylene or an epoxy resin which has been screenprinted onto can periphery 22. A separate cross-linked butyl rubbermaterial 36 is included within seal 32a. Such can be a separatepreformed butyl rubber gasket, or in situ formed in place atop gasket34a, as will be more fully explained below.

As an alternate embodiment, seal materials 34, 34a or 36 can preferablycomprise a chemical precursor to formation of butyl rubber. Examplebutyl rubber precursors include isobutylene, isoprene or a mixturethereof. Further, such chemical precursors to formation of butyl rubbercan preferably comprise depolymerized butyl rubber. An exampledepolymerized butyl rubber material is Kalene 800, available fromHardman, a division of Harcros Chemicals, Inc. of Belleville, N.J.

Such material can be utilized without addition of any supplementalcuring or cross-linking gent which would transform such material into abutyl rubber. Further in accordance with the example FIG. 3 embodiment,material 34a of seal 32a could comprise a pre-formed gasket consistingessentially of butyl rubber, with material 36 comprising depolymerizedbutyl rubber which is in contact therewith.

With respect to utilization of an ultimately uncured chemical precursorto butyl rubber, such could be provided relative to a first terminalhousing member either before or after the first terminal housingmember's shape has been completed. An example process of utilizing suchmaterial prior to shaping of first terminal housing member 18 isdescribed with reference to FIGS. 4-6.

Specifically, a continuous electrically conductive first terminalhousing member material sheet 50 from which first terminal housingmember 18 will be formed is provided. An electrically insulativechemical precursor material 34 to formation of butyl rubber is depositedrelative to what will be a sealing region of the first terminal housingmember. Such deposited precursor, in accordance with this example aspectof the invention, is void of any polymerizing or curative agents suchthat the precursor remains substantially un-polymerized upon processcompletion. The preferred materials are again isobutylene, isoprene,mixtures thereof, or depolymerized butyl rubber such as the Kalene 800.

The deposited material might also preferably comprise some viscosityreducing solvent to facilitate initial flow and deposition of material34. Example solvents include hexane, toluene, and methyl ethyl ketone.Prior to assembly, and most preferably prior to cutting and forming, theviscosity reducing solvent will substantially evaporate to raise theviscosity of the deposited precursor material 34. Were a battery of theFIG. 3 construction being formed, a layer 36 would at this point in theprocess have been deposited atop a preapplied or preset gasket 34a whichcould comprise butyl rubber or some other material.

Sheet 50 is passed through a cutting and forming station 52. There, aplurality of discrete first terminal housing members 18 are sequentiallycut to form resultant first terminal housing members 18. Station 52comprises a cutting and forming tool including a ring die cutter 54. Acentral forming press 56 is sized to engage sheet 50 as it is cut asshown. FIGS. 5 and 6 illustrate one example first terminal housing 18which has been formed into a shape of a desired first terminal housingmember.

Referring to FIG. 7, anode 12, cathode 14, electrolyte 16, separator 17,first terminal housing 18 and second terminal housing 24 are shown in apre-assembly exploded view. The first and second terminal housing memberperipheral areas 22 and 28 comprise a sealing region for the battery. Ina preferred embodiment (not shown), the figure would be inverted, withanode 12 being previously adhered to second terminal housing 24 withelectrolyte 16 and separator 17 received therein.

Referring to FIG. 8, first and second terminal housing members 18 and 24are pressed together and sealing portion 22 of first terminal housing 18is initially bent inwardly to begin the crimping. Bending continues toproduce the finished FIG. 2 construction such that the sealing regionsare joined and a battery housing is formed.

A similar process can be utilized to produce the desired battery havinga resultant butyl rubber containing seal. Specifically, an uncuredelectrically insulative chemical precursor material to formation ofbutyl rubber can be deposited relative to a sealing region of a firstterminal housing member in either a sheet shape or can shape. Thedeposited uncured precursor material would comprise an appropriatecurative and polymerizing agent capable of curing the deposited materialinto polymerized cross-linked butyl rubber. Examples are provided below.The inventive method further comprises in situ curing the chemicalprecursor material with such agent into butyl rubber. Such curing mightbe, in one example, substantially completed before joining the sealingregions of the first and second terminal housing members to form theresultant enclosed battery housings. Alternately, the chemical precursormaterial might be substantially uncured at the point of combining withthe second terminal housing member, with the curing not beingsubstantially completed until after joining. Further at the time ofdeposition relative to a first terminal housing member, the depositedprecursor material including precursor and curative agent might comprisea viscosity reducing solvent which ultimately evaporates. Further, thedeposited precursor and curative agent could be deposited directly to afirst terminal housing member material or to gasket material previouslyprovided thereto, such as existing formed butyl rubber or anothersuitable insulating gasket material.

Accordingly, one example preferred method in accordance with theinvention includes in situ formation of butyl rubber relative to thefirst terminal housing member, as opposed to previous butyl rubberformation and subsequent application to a first terminal housing member.Further, a chemical precursor to butyl rubber formation might beutilized as a primary final inherent gasketing material, or as asupplemental sealant or adhesive material utilized in conjunction withsome other primary gasket which may or may not comprise or consistessentially of butyl rubber.

The following are examples of possible formulations for curable,polymerizable and cross-linking materials which can be depositedrelative to a first terminal housing member for ultimate in situ curinginto polymerizable rubber.

FORMULA #1

Kalene 800=100 parts

Quinone dioxime=2 parts

Lead peroxide (PbO₂)=4 parts

FORMULA #2

Kalene 800=100 parts

Quinone dioxime=2 parts

Lead tetraoxide PB₃ O₄ =8 parts

FORMULA #3

Kalene 800=100 parts

Quinone dioxime=2 parts

Lead tetraoxide=6 parts

Benzothiazyl disulphide=4 parts

FORMULA #4

Kalene 800=100 parts

p-(dibenzoyl quinone dioxime)=6 parts

Lead tetraoxide=10 parts

FORMULA #5

Kalene 800=100 parts

Quinone dioxime=1 part

Benzothiazyl disulphide=2 parts

Tetrachloro-p-benzoquinone=1 part

FORMULA #6

Kalene 800=100 parts

Quinone dioxime=2 parts

Zinc oxide (uncoated)=2 to 5 parts

FORMULA #7

Kalene 800=100 parts

Quinone dioxime=2 parts

Calcium oxide=2 to 5 parts

The quinone dioxime comprises a non-sulfur vulcanizing agent for thevarious formulations. Lead tetraoxide functions as an activator.Para-dibenzoyl quinone dioxime also functions as a non-sulfurvulcanizing agent. Additional possible sealants might also be utilized.The above formulations will all cure into butyl rubber at roomtemperature, with the rate of curing decreasing as one proceeds fromFormula #1 to Formula #7. With the above formulas, both the working lifeof the mixture (the viscosity change) and the time it takes to full cureincrease in progressing from Formula #1 to Formula #7.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

I claim:
 1. A method of forming a thin profile battery defined by athickness which is less than a maximum linear dimension of its anode,the method comprising the following steps:providing an electricallyconductive first terminal housing member material; depositing anelectrically insulative unpolymerized chemical precursor material toformation of butyl rubber relative to a sealing region of the firstterminal housing member material, the deposited precursor material beingvoid of any polymerizing or curative agents; after the depositing step,providing the first terminal housing member material into a shape of adesired first terminal housing member; providing an electricallyconductive second terminal housing member in facing juxtaposition to thefirst terminal housing member having the deposited butyl rubberprecursor material, the second terminal housing member having a sealingregion; providing an anode and a cathode having an electrolytepositioned therebetween; the anode, the cathode, and the electrolytebeing positioned intermediate the juxtaposed first and second terminalhousing members; the anode being positioned to electrically connect withone of the first or second terminal housing members and the cathodebeing positioned to electrically connect with the other of the first orsecond terminal housing members; providing a preformed gasket, thegasket consisting essentially of butyl rubber, the depositing stepcomprising applying the chemical precursor material onto the pre-formedbutyl rubber gasket; and joining the sealing regions of the first andsecond terminal housing members together to form an enclosed batteryhousing retaining the anode, the cathode and the electrolyte; theelectrically insulative butyl rubber precursor material void of anypolymerizing and curative agents being interposed between the joinedfirst and second terminal housing members; the precursor materialbetween the joined first and second terminal housing members comprisingan electrically insulative fluid-tight seal therebetween; the insulativeseal comprising the pre-form butyl rubber gasket and the unpolymerizedbutyl rubber precursor material.
 2. A method of forming a thin profilebattery defined by a thickness which is less than a maximum lineardimension of its anode, the method comprising the followingsteps:providing an electrically conductive first terminal housing membermaterial; depositing an uncured electrically insulative chemicalprecursor material to formation of butyl rubber relative to a sealingregion of the first terminal housing member material, the depositeduncured precursor material comprising a curative and polymerizing agentcapable of curing the material into polymerized cross-linked butylrubber, the method comprising in situ curing of the chemical precursormaterial into butyl rubber; after the depositing step, providing thefirst terminal housing member material into a shape of a desired firstterminal housing member; providing an electrically conductive secondterminal housing member in facing juxtaposition to the first terminalhousing member having the deposited butyl rubber precursor, the secondterminal housing member having a sealing region; providing a pre-formedgasket, the gasket consisting essentially of butyl rubber, thedepositing step comprising applying the chemical precursor material ontothe pre-formed butyl rubber gasket; providing an anode and a cathodehaving an electrolyte positioned therebetween; the anode, cathode, andelectrolyte being positioned intermediate the juxtaposed first andsecond terminal housing members; the anode being positioned toelectrically connect with one of the first or second terminal housingmembers and the cathode being positioned to electrically connect withthe other of the first or second terminal housing members; and joiningthe sealing regions of the first and second terminal housing memberstogether to form an enclosed battery housing retaining the anode,cathode and electrolyte comprising an electrically insulativefluid-tight seal therebetween; the insulative fluid tight sealcomprising the preformed butyl rubber gasket and in situ formed butylrubber; the chemical precursor material being provided to besubstantially uncured at the joining step, the curing not beingsubstantially completed until after the joining step.